Acetaminophen (APAP, N-acetyl-p-aminophenol, paracetamol) is the leading analgesic and antipyretic drug used in the United States. Acetaminophen is well tolerated, lacks many of the side effects of aspirin, and is available without prescription.
It is well-established that large acetaminophen overdose causes hepatotoxicity and in rare cases nephrotoxicity in humans and in experimental animals. Acute overdosage of acetaminophen results in dose-dependent and potentially fatal hepatic necrosis as well as in rare cases renal tubular necrosis and hypoglycemia.
At recommended dosages, most ingested acetaminophen is metabolized by sulfation and glucoronidation to form non-toxic metabolites which are excreted in the urine. A small percentage, generally estimated at less than 5%, is metabolized in the human liver by microsomal cytochrome P-450 to a metabolite, believed to be N-acetyl-p-benzoquinone imine (NAPQI). NAPQI bonds covalently to cellular constituents irreversibly arylating critical cellular proteins and causing cell death.
At therapeutic doses of acetaminophen, the small amount of NAPQI formed is detoxified prior to arylating cellular proteins by preferential conjugation or reaction with hepatic glutathione (via sulfhydryl groups). Subsequently, the detoxified NAPQI is excreted in the urine as conjugates of cysteine and mercapturic acid. However, when acetaminophen is taken in a large overdosage, glutathione stores may become depleted and hepatic necrosis may occur.
Recently, certain immunohistochemical studies have suggested that NAPQI-protein adducts appeared even at sub-hepatotoxic acetaminophen doses and before depletion of total hepatic glutathione. (Roberts et al., "Immunohistochemical Localization and Quantification of the 3-(cystein-S-yl)-Acetaminophen Protein Adduct in Acetaminophen Hepatotoxicity", Am. J. Pathol. 138:359-371 (1991)). It has been suggested that the formation of such NAPQI-protein adducts may be related to rare cases of hypersensitivity. (Stricker and Meyboom, "Acute Hypersensitivity Reaction to Paracetamol", Br. Med. J. 291:938-939 (1985); Hurvitz et al., "Acetaminophen Hypersensitivity Resembing Kawasaki Disease", Israel J. Med. Sci., 20:145-147 (1984)).
In the human liver, microsomal cytochromes P-450s 2E1 and 1A2 appear to be the two major enzymes responsible for the bioactivation of acetaminophen. (Raucy et al., "Acetaminophen Activation by Human Liver Cytochromes P450IIE1 and P450IA2", Arch. Biochem. Biophys. 271:270-283 (1989)). Studies in mouse kidney have also suggested that P-450 2E1 plays an important role in the bioactivation of acetaminophen (e.g., the conversion of acetaminophen to NAPQI (Hu et al., "Sex-Related Differences in Mouse Renal Cytochrome P450IIE1: Effects on the Metabolism and Nephrotoxicity of Acetaminophen, FASEB J 5:Abstract (1991)).
Early treatment of acetaminophen overdosage is considered to be crucial, and vigorous supportive therapy is essential when intoxication is severe. It is recommended that induction of vomiting or gastric lavage be performed in most cases when less than 24 hours has elapsed since overdose.
Protective agents for acetaminophen overdose have been extensively studied. A known method of treatment is the administration of sulfhydryl compounds. L-methionine, L-cysteine, and N-acetylcysteine are known to have a protective action in animals. Methionine and another sulfhydryl compound, cysteamine (possibly a source of sulfate for conjugation), have been reported to provide some protection (see, e.g., Prescott et al., "Cysteamine, Methionine, and Penicillamine in the Treatment of Paracetamol Poisoning", Lancet, 2:109-113 (1976)). N-acetylcysteine is considered to be effective when given orally. Also, cimetidine, dimethyl sulfoxide, and ethanol have been shown to inhibit acetaminophen bioactivation. Early administration of compounds supplying sulfhydryl groups (0 to 10 hours after acetaminophen ingestion) may prevent or minimize hepatic injury in cases of acetaminophen overdose.
The inventor has demonstrated that diallyl sulfide (DAS), a compound contained in garlic, is metabolized to diallyl sulfoxide (DASO) and diallyl sulfone (DASO.sub.2) (Brady et al., "Inhibition of Cytochrome P-450IIE1 by Diallyl Sulfide and its Metabolites", Chem. Res. Toxicol. 4:642-647 (1991)). Treatment of rats with these compounds decreased liver microsomal P-450 2E1-dependent, e.g. N-nitrosodimethylamine (NDMA) demethylase, activity. The decrease by DASO.sub.2 was found to occur more rapidly than by DAS or DASO (Brady et al., "Effect of Diallyl Sulfide on Rat Liver Microsomal Nitrosamine Metabolism and Other Monooxygenase Activities, Cancer Res. 48:5937-5940 (1988); Brady et al., "Modulation of Rat Hepatic Microsomal Monooxygenase Activities and Cytotoxicity by Diallyl Sulfide", Toxicol. Appl. Pharmacol. 108:342-354 (1991)). Furthermore, in isolated rat liver microsomes, DAS, DASO, and DASO.sub.2 inhibited P-450 2E1-catalyzed (NDMA) demethylase and p-nitrophenol hydroxylase (e.g., p-nitrophenol hydroxylase) activities competitively, and DASO.sub.2 also caused a metabolism-dependent inactivation (Brady et al., "Inhibition of Cytochrome P-450IIE1 by Diallyl Sulfide and its Metabolites", Chem. Res. Toxicol. 4:642-647 (1991)). DAS has also been shown to protect toxicity associated with carbon tetrachloride hepatotoxicity (Brady et al., "Modulation of Rat Hepatic Microsomal Monooxygenase Activities and Cytotoxicity by Diallyl Sulfide", Toxicol. Appl. Pharmacol. 108:342-354 (1991)), and 1,2-dimethylhydrazine-induced hepatotoxicity and carcinogenesis in rats (Hayes et al., "Inhibition of Hepatocarcinogenic Responses to 1,2-Dimethylhydrazine by Diallyl Sulfide, a Component of Garlic Oil" Carcinogenesis (Lond.) 8:1155-1157 (1987); Wargovich, "Diallyl Sulfide, a Flavor Component of Garlic (Allium Sativum), Inhibits Dimethylhydrazine-Induced Colon Cancer", Carcinogenesis (Lond.), 8:487-489 (1987)). It has been demonstrated that pre-treatment of rats with DAS, DASO.sub.2 or disulfiram inhibited the hepatotoxicity of CCI.sub.4 and N-nitrosodimethylamine; both are substrates of P450 2E1 (Yang, et al., "Cytochrome P450 2E1: Roles in Nitrosamine Metabolism and Mechanisms of Regulation", Drug Metab. Rev., 22:147-160 (1990)).